土壤脲酶活性对稻田田面水氮素转化的影响

以浙江省嘉兴市双桥农场的青紫泥水稻田为研究对象，采用大田小区的研究方法，对不同供肥水平下水稻追施尿素后田面水中氮素主要形态的浓度变化进行了动态监测，并从土壤酶学的角度探讨了其氮素转化的深层机制。研究发现．土壤脲酶在稻田田面水氮素转化中起着关键作用，施尿素后3天内田面水中总氮、氨氮的浓度及氨氮／总氮比值达到峰值．且第二次追肥较第一次追肥后峰值低．随后急剧下降。5天后维持在较低的水平，说明施肥后前5天是氮素大量且快速流失的关键时期，其流失以氨氮为主；土壤脲酶活性在第一次追肥后3～5天也出现了明显的增长趋势，第二次追肥后脲酶活性增强幅度远小于第一次追肥．N270处理初期甚至出现了负增长；线性相关分析表明田面水中氨氮／总氮的比值与土壤脲酶活性之间存在显著的正相关关系．说明土壤脲酶在水土界面氮素迁移转化过程中发挥着关键作用，因此，抑制脲酶活性可能是降低稻田氮素流失的主要途径之一。

Influence of Soil Urease Activities on Nitrogen Conversion in Floodwater in Paddy Field

The dynamic changes of main nitrogen forms in floodwater of paddy field under different fertilizer rates was studied in Shuangqiao farm,Jiaxing city,Zhejiang province.Soil urease activities was used to explain the mechanisms of nitrogen conversion in floodwater.The results showed that total nitrogen(TN) and ammonia nitrogen(NH~ _4-N) concentration and the ratio of ammonia nitrogen and total nitrogen(NH~ _4-N/TN) in floodwater of each treatment boosted up during the 1~3 days after fertilization and the peak values after the 2nd topdressing was lower than that after the 1st topdressing,and then decreased drastically,maintained at relatively low level after 5 days;it was proved that the first 5 days after fertilization was the most important period of nitrogen especially ammonia nitrogen loss.There was the similar trend of soil urease activities with nitrogen in floodwater.According to the linear correlation analysis,the relationship between NH~ _4-N/TN in floodwater and soil urease activities reached the remarkable and positive relevant level.It was indicated that soil urease activities played a key role in nitrogen conversion in soil-water interface of paddy field.